There is in the human mind a tendency to personify abstractions. These ideal types have usurped a place in the domain of facts, so that a real existence has been given to them. The monogenists had, strictly speaking, a right to do so without any violence to their principles; but the polygenists, who have followed their example, have sinned against logic. The former attribute all varieties of the human species to the numerous modifications of five _principal_ races, issued themselves from one common stock, and the same influences which, according to then, have in the origin produced fundamental races, have afterwards by an analogous process produced the _secondary_ races. All this is sufficiently clear; and such stood the question when the polygenists appeared in the arena. Their first efforts were directed to attack the doctrine in its essential foundations, and to demonstrate that by no natural causation could Whites be transformed into Negroes, or Negroes into Mongolians; they therefore proclaimed the multiplicity of human origin and the plurality of species. Be it that they have shrunk from the idea of causing too great a revolution in science, or that they thought that it would conduce sooner to the triumph of their doctrine, they retained as far as possible the number of species, and confined themselves to assume a primitive stock for each of the five races described by the Unitarians. I do not assert that all polygenists followed this course, as some proceeded in a more independent manner. Bory de Saint-Vincent, Desmoulins, P. Bérard, Morton, had the courage to break entirely with the past, and to remodel the classical divisions. They found, however, but few imitators; and many polygenists are to this day content to assign a distinct origin to each of the five principal trunks, which constitute for the monogenists the five fundamental races, but which are to us only natural groups formed by the union of races or species of the same type. They continue also very often to use the term _race_ to designate the _ensemble_ of all individuals of each group, adopting thus by a sort of transaction the language of those whose system they reject; and thus they speak of the white or Caucasian race, the yellow or Mongolian race, the black or Ethiopian race, etc., as if all these individuals of a Caucasian type resembled each other to constitute one race; as if, for instance, the brown Celts and the fair-haired Germans had descended from the same primitive stock. This contradiction has given a handle to the monogenists; for if climate and mode of life may cause a German to become a Celt, there is no reason why, under certain influences, a Celt might not become a Berber, a Berber a Foulah, a Foulah a Negro, and a Negro an Australian.